BAITED UNDERWATER VIDEO
Ever wondered how scientists count fish?
One method that is used widely around New Zealand and the world is Baited Underwater Video (BUV).
This method uses bait to attract fish in front of a camera. Researchers can then count the fish on the video to get an idea of species abundance and diversity.
HOW IT WORKS
HOW IT LOOKS
The BUV we use has a metal frame that holds a camera overlooking a bait pot. On the lower arm of the frame, there are black marks which give the observer an idea of how big the fish are. Each mark is 10cm long.
The top of the frame is tied to two floats. One of the floats is underwater with the frame and helps to keep the frame upright. The other float is on the surface and is to help the boat find the camera again when the trial is over.
HOW IT RUNS
To run a BUV trial, researchers lower the frame over the side of the boat. When the frame touches the seafloor the trial begins. We run our BUV trials for 30 minutes. Once the time is up, you pull the BUV back to the surface and download the video footage for analysis.
When researchers do a BUV survey of an area, they will repeat this process over and over in different locations. The more replications (or trials) you do, the more confident you can be that your results are accurate.
Q&A ROUND 1!
A. Some areas may be too deep or dangerous for divers to investigate.
A. Some fish behave differently when divers are in the water. Fish could be scared off by a diver and therefore not counted. Sometimes fish are attracted to divers and follow them around, this might mean they get counted more than once!
Q. Why do you think some researchers use remote cameras instead of having SCUBA divers count fish in an area?
Q: Do you think this method can be used to investigate all fish?
Or is it limited to certain types of fish?
A: This method focuses on fish that are carnivorous and are attracted by bait. It would not be a good method if you wanted to know more about herbivorous fish.
Q. What are two things that you would want to keep the same during every trial of a BUV survey?
A. Trial length. You want to make sure that all your trials are the same length of time.
A. Bait amount and type. It’s important to use the same amount of bait every trial. If you used 400 grams of bait in one trial and only 200 grams of bait in another trial, that wouldn’t be a fair comparison. You also want to keep the type of bait you use consistent.
Pākirikiri, Rāwaru Parapercis colias
For our BUV's, we're analysing the number of Blue Cod!
Why Blue Cod you ask? Well, firstly they're endemic to New Zealand and inhabit open reef areas or sand and gravel near patch reefs... it's also one of the most common caught recreational fish in South Taranaki, and our fishing survey's indicated Project Reef as a possible Blue Cod nursery!
3 COLOUR PHASES
Scroll over each image to discover the three colour phases of Blue Cod!
A big thank you to Dr Malcom Francis who's wonderful book 'Coastal Fishes of New Zealand' contains the following images of & information on Blue Cod!
Coastal Fishes of New Zealand has been Project Reef's 'go to' book for identification, biology & behaviour for fish!
(Up to about 10cm long)
White with 2 dark brown or black stripes on the back, one of which continues through the eye and onto snout.
(Fish 10 - 25cm long)
Stripes fade to light brown and become less distinct.
(Fish over 25 - 30cm)
Blue-grey above with turquoise band behind head, and white tail below; tail, upper head and upper lip dark grey.
TRY IT YOURSELF!
When we watch BUV footage, there is no way of knowing if the fish that swims in during the first minute is different from a similar-looking fish that swims in 5 minutes later. We don’t want to be counting the same fish twice! To avoid this, we take the one frame of the video that has the most fish in it and use that as our count for that trial.
You can try doing this for the video below. Try pausing the video every 30 seconds and counting the number of blue cod. You could even pause it every 10 seconds if you wanted to be more accurate!
LET'S GET TO WORK!
Ever wondered how scientists count fish? One method that is used widely around New Zealand and the world is Baited Underwater Video (BUV).This method uses bait to attract fish in front of a camera. Researchers can then count the fish on the video to get an idea of species abundance and diversity.
Snapper eat virtually any animal matter, and diet changes with size.
One of the largest carnivores on the reef is the octopus!
SEVEN GILL SHARK
These sharks investigate objects by bumping them with their snouts.
These fish have three colour phases... juvenile, female and male.
These sharks are nocturnal, usually sluggish & are not dangerous.
Q&A ROUND 2!
A. Because that would mean we could be overestimating the number of fish in that area.
Q. Why do we want to avoid counting the same fish twice?
Q. Could there be problems with multiple people analysing different videos in a BUV survey?
A. Some people are better at counting fish than others so it could make the results unfair. The best way is for one researcher to do all of the video analysis in a BUV survey. It’s not realistic to have one person to do this for every survey though. This is one limitation that we have to live with. The more videos you analyse the better you get at spotting the fish!
Q. Why do we want to measure the fish using the marks on the frame?
A. It’s important for us to know how many of the fish are juvenile (young) and how many are adults. This can help to monitor how the health of the population changes over time.
MORE BUV RESOURCES
Hagfishes (Myxinidae) are a family of jawless marine pre-vertebrates. Using baited remote underwater video systems, it was revealed that hagfishes are able to choke their would-be predators with gill-clogging slime! Find out more about
the work of Vincent Zintzen, Clive D. Roberts, Marti J. Anderson, Andrew L. Stewart, Carl D. Struthers & Euan S. Harvey's work on Hagfish predatory behaviour and slime defence mechanism!